Liquid clarification apparatus



` Aug- 15, 1944. Y A. J. FISCHER ,E1-Au 2,355,640

LIQUID CLARIFICAT ION APPARATUS Filed May l2, 1942 5 Sheets-Sheet l F'IGJ.`

ANTHONY J. FISCHER 8| WILLIAM C. WEBER ATTORNEY Aug- 15, 1944- A. J. FISCHER ET A1. 2,355,640

LIQUID CLARIFICATION APPARATUS Filed May 12, 1942 3 Sheets-Sheet 2 Aug- 15, 1944- A. J. FlvscHER ET AL 21,355,640,

LIQUID CLARIFICATION APPRATUS Filed May l2, 1942 3 Sheets-Sheet 3 INVENTORS r ANTHONY J. FISCHER FIG 7 WILLIAM C. WEBER BY MM ATTORNEY Patented Aug. 15, 1944 Anthony J. Fischer, Manhasset, N. Y., and

William C.' Weber, Westport, Conn., assignors to The Dorr Company, New York, N. Y., a corporation of Delaware Application May 12, 1942, Serial No. 442,638-

(ci. 21o-.n

1o claims.

The invention hereof primarily relates to and revolves about a novel form of clarification or thickening apparatus embodying a single tank 4structure having a liquid-holding section that is divided by a partition vor partitioning means into functionally separated pirmary and secondary compartments that are in constant hydraulic communication through a passage area left because of the partition being only a partial one and certain other parts or features arranged in novel functioning relationship with respect thereto.

The tank structure or tank has a bottom, preferably with a depressed portion providing a sump,

and a marginal wall rising from the bottom whereby a liquid-holding section is provided within the tank. In the form of constructionillus' trated .this sump is located at the bottom of the primary compartment. This is the preferred location for the sump. However, according to certain broad aspects of the invention the sump, if provided, is not necessarily located immediately below the primary compartment. The tank is preferably equipped with suitable sediment-collecting and transferring mechanism that includes sediment-engaging and impelling elements which are operable over the floor or bottom of the tank and functionable to transfer 4sedimented material engaged thereby towards and into the sump. The sump has sediment-withdrawal means for from time to time passing sedimented material therefrom to the exterior of the tank.

In the form of construction shown the tank is rectangular in plan and is equipped with a sediment-transfer mechanism embodying a conveyor of the endless type with a lowermost section or lowly positioned conveying element that is movable longitudinally and along the oor or bottom of the secondary compartment through the passage area below or provided by the partitioning means and continues along the oor or bottom of the pirmary compartment until it has delivered the sludge transferred thereby into said sump. The tank-preferably the primary "compartment thereofmay be provided with a scumrecciving troughand the conveying means referred to may also include a scum-transferring element disposed for operative association with the scum trough whereby the scum-transferring element can convey or push floating scum engaged thereby towards and into said trough.

According to the inventiona feed-receiving and distributing. means is provided for the primary compartment, and a collecting launder or other suitable collecting means is provided for receiving supernatant liquid passing thereinto from the upper interior portion of the primary compartment. p

In the rectangular form of .tank illustrated it is divided bya vertically and transversely-extending partition terminating a distance above the bottom of the tank so that the primary and secondary compartments havey horizontal disposi-l tion and are in constant hydraulic 'communication whereby there is a common level for the liquid in both compartments. This collectnig launder or means is forwardly spaced a substantial horizontal distance from the feed-receiving and distributing means and Where a scum trough is employed the collecting launder is preferably disposed between the partition` and the scum trough. In other words, the horizontal spacing or arrangement just referred to calls for the feed-receiving and distributing means being located at the rear or receiving end of the tank, the collecting launder orv collecting meansproximate or in rear of the partition and the scum trough between the two preferably close to but somewhat in the rear of the collecting launder.

As to the secondary compartmenathis has a liquid feed-distributing means preferably close to or immediately ahead of the partition and an eluent launder horizontally spacedy from the liquid feed and distributing means, preferably at 3o the front or effluent `discharge end of the tank.

This eflluent launder, or liquid overflow means as it may be sometimesreferred to, has an overflow edge or section at sufcient height or elevation to determine the normal surface level of Vthe liquid within the tank.

t The clarification tank or thickening apparatus which has just been referred to has been designed primarily for use in sewage disposal systems wherein there is employed in cyclic arrangement with the tank or thickening-apparatus a biologic treating means essentially embodying a bed or beds of discrete material having biologically active organisms therein or, as otherwise expressed, having biologically active organisms upon the surface of the descrete material con'- stituting the bedor beds. This novelform of tank is arranged and employed in a novel manner in association with. such biologic treating means as will hereafter more fully appear. The

5o clarification tank or thickening unit comprising the tank has use, however, in other fields and the tank and the parts associated therewith can be broughtinto novel operative relationship in diverse ways as will be manifest from that follows which ./f

In each form illustrated some of the liquid collected from the primary compartment by the collecting launder or means referred to is ultimately passed by suitable means that include piping, pumping means1 and some form of biologic treating means into the feed-distn'buting means for the subsequent compartment. In other words, means is provided whereby some of the liquid from the collecting launder of the primary compartment is pumped and delivered into the feed-distributing means of the secondary compartment. According to certainv of the arrangement illustrated some' of the liquid from the primary collecting launder or means may be passed for a biologic treatment through only one bed of discrete material, while according to other arrangements it may be subjected to treatment in a plurality of beds before ultimate delivery into the feed-distributing means for the secondary compartment. Such bed provides biologically active organisms that decrease the biologic oxygen demand of polluted liquid passing therethrough. From that which will follow one will see that various modes of flow and distribution is obtained or realized by the piping arrangement or systems shown, each and all of which will be. more clearly brought out in conjunction with the specic description relating to the systems or owsheets hereinafter referred to.

Other features of construction and further objects and functional aspects of the invention will be manifest and brought out by the detailed description that follows and are particularly pointed out in and by the appending claims.

In the following description and in the claims parts will be identified by specific names for convenience but they are intended to be as generic in their application of similar parts as the art will permit.

In the accompanying drawings which constitute a part of this specification, there have been illustrated the best and most characteristic embodiments of the invention known to the undersigned, but such embodiments are tobe regarded as typical only of many possible embodiments and the invention is not to be limited-thereto.

In said drawings:

Fig. 1 is a plan viewpartially in horizontal section-of a sewage treating system wherein the plural-compartment rectangular tank is operatively connected in. association with a laterally disposed biologic treating means having a single bed of discrete material, to wit, a biologic treating bed which is in the form of a trickling filter.

Fig. 2 is a view showing the tank in vertical longitudinal section, to wit, primarily as a view taken on the vertical plane indicated by the broken line 2 2 of Fig. 1, looking in the direction of the arrows. In this figure, however, a portion of the tank structure has been broken away so as to show the relative vertical elevation of the trickling ilter which is laterally disposed with respect to the tank structure. In this connection it will be noted the trickling filter is at elevation substantially lower than that of the normal surface level of the liquid within the tank and that the trickling lter is shown in vertical section.

Fig. 3 is a detailed vertical sectional viewillustrating more clearly the central portion of the tank in the region of the vertically and transversely extending partial partition of the tank.

Fig. 4 is a plan view of the same type of pluralcompartment tank connected in operative association with a laterally disposed biologic treating means provided by a single trickling filter.

Fig. 5 is a vertical sectional view of the tank taken as on the vertical plane indicated by the broken line 5--5 of Fig. 4 looking in the direction of the arrows. In Fig. 5 a certain portion of the side wall of the tank has been broken away to show a basin or well providing a liquid commingling member. In the case of Figs. 4 and 5 the trickling filter is at elevation substantially above that of the normal surface level of the liquid within the tank. The trickling filter in this instance is also shown in vertical section.

Fig. 6 is a plan view showing the plural compartment-tank connected in operative arrangement with laterally disposed biologic treating means provided by two spacedly positioned trickling filters.

Fig. '7 is a vertical sectional view of the tank taken as on the vertical plane indicated by the broken line 'I--l vof Fig. 6 looking in the direction of the arrows. In this view the laterally disposed trickling filters are at elevation higher than that of the tank and are shown in vertical section.

Reference will now be made to the drawings in detail:

Like reference characters indicate parts functioning the same or substantially alike wherever they appear.

The plural compartment tanks The tanks employed in each of the sewage treating systems illustrated are substantially the same` except that no scum weir is-shown in the form illustrated in Figs. 4 and 5. It is shown,

` however, in the other figures.

The tank or tank structure generally designated by I0 has a bottom section or floor providing member II having a depressed portion I2 providing a sediment-receiving section or sump I3. The tank also has a marginal wall I4 rising from the bottom I I. This marginal wall includes .a vertically and transversely extending rear end of the tank whereby it, with the spaced side walls of the tank, and with the underlying floor portion of the tank constitute means providing and defining a flow passage area 2| leading rearwardly from the liquid-holding section or compartment 23 which is functionally ahead of the partition toand into the liquid-holding section or compartment 22 which is at the rear of the partition. In other words, this partial partition divides the tank into functionally separated-primary and secondary quiescent liquid-clarifying zones or compartmentsheretofore respectively designated as 22 and 23. These compartments are in constant hydraulic communication with each other through the passage area 2| referred to. The primary compartment 22 is at the feedreceiving. end of lthe tank and the secondary compartment is at the front or eluent discharge end of the tank;

The primary compartment has a feed-receiving and distributing means collectively designatedas 2l, and which is provided by a feedreceiving and distributing launder 25 and a baffle member 26. downwardly from the top portion of the tank a. substantial distance within the liquid-holding section of the tank and it is forwardly spaced'4 with respect to the rear end or wall I of the tank to provide a downwardly directed flow-path 21 whereby the incoming liquid is localized within the rear or receiving end ofthe tank until it is distributed into and across-the lower rear' end portion ofv the primary compartment 22.

This flow-path 21 immediately overlies the sump I3 whereby any quickly settleable solids can drop immediately into thev sump. A sediment-discharge conduit 28, controlled as by a stopvalve` or gate 29, leads from the sump I3, or as otherwise expressed, from the lower interior compartment 22. This valve-controlled conduit 28 is relied upon for passing, accrdingto voperative requirements, sedimented material received within the sump I3.`

The primary compartment` 22 is also provided with a collecting launder 30 that is preferably disposed immediately behind` the partial partii tion I9 and which is at elevation for receiving' This baiiie member 26 extends` CII ' the scum trough 51 referred to.

the collecting launder 30 it is sometimes referred' to as a submerged collecting means or member for the Iprimary compartment 22. The liquid collected thereby may* be supernatant liquid or liquid material taken from any elevation in the tank and may even contain a considerable portion of solid materialsuch as is delivered from the secondary compartment by the sludge-'cob' lecting means.

As to the secondary compartment this hasa liquid-receiving and distributing means c ollec` tively designated as 3 I. This distributing means embodies a receiving launder 32 and is preferably provided with a baffle 33 that is spaced a short distance ahead of the launder 32 whereby a downwardly directed flowpath 34 is provided from which downowing liquid is distributed Within and across the lower rear end portion of the secondary compartment 23. At they forward 0r discharge end of the tank there lis provided an eiliuent launder 35 for receiving supernatant liquid of the secondary compartment. This launder 35 has an overilowweir or edge 36 that determines the normal surface level of the liquid within the tank.- Means in the form of a pipe or outow conduit is provided at 31 by which liquid overflowing into the launder 35 may be passed therefrom and it is from this' tube or conduit that liquid is released from the system in quantity corresponding to the quantity of feed supplied for treatment.

The co-mpartments 22 and 23 provide horizontally disposed quiescent sedimentation'zones and it will be clear that settleable material can gravitate from the liquid therein and deposit as sediment or sludge on the underlying floor portion or bottom of the tank. In order to effect a progressive` transfer of this sedimented material from diverse sections of the tank bottom to and into said sump there has been provided an end- .ing Opening for the scum passed thereto.

less 4type of conveyor collectively referred to as 4U. This conveyor embodies transversely spaced endless members as endless chains 4| and supporting sprockets or guiding wheels therefor as 42, 43, 44, 45 and 46. These endless chains 4I have connected thereto transversely extending sediment-impelling elements in the form of Scrapers `or raking blades 41. These scraping elements extend across or transversely of the tank over the floor or bottom thereof and are longitudinally s-paced'with respect .to each other and are carried by the endless members 4I. Each endless chain 4I comprises a forwardly movable'upper section or strand 50, a descending vertical section 5I, a forwardly movable longitudinal. section 52 disposed at elevation for passing `below the lower edge of the partition I9 without interference therewith, a lowermost section 53 movable rearwardly along and immediately over the bottom II of the tank and a rising vertical section 54 reaching to the upper section 50. A transversely extending vertical baille 48 is disposed between the descending section 5 I and the overflow edge 49 of the collecting launder 3I'I.l In a tank structure where a scum launder as` 51 is employed this baille is located between the scum launder 51 and the edge 4 9 of the .collecting launder 30. .A

In the forms shown in Figs. 1 to 3 and in the forms shown in Figs. 6 and 7, there is indicated In the form shown the scum trough Aembodies a cylindrical member 58 slotted at the top to provide a receiv- This cylindrical member is mounted in seats 59 and has a handle Gilwhereby the position of `the slotted `portion of the trough 51 relative tothe `general level in the tank can be adjusted. Scum The system of Figures 1 to 3 In this system` the biologic treating means is in the form of a trickling filter having a bed of discrete material 10 within a containingr structure 1I having a collecting section 12 for receiving lter eilluent.` As this trickling filter bed is at elevation substantially lower than that of the general level ofthe liquid in the tank, liquid can flow by gravity from the collecting launder 30 through pipe or conduit 13, and from the effluent launder 35 through the pipe or conduit 15, and from the pipes 13 and 15, which may be viewed as branches, to a lateral main pipe 11 and upow pipe 18 then@ into a rotary distributor 19 by :which any liquid flowing thereinto is relatively v uniformly distributed over` the trickling filter bed. The pipe 13 is provided with a positionablel trolled pipe 15, pipe sections 11 and 18 and the rotary distributing head 19 may be viewed as means for selectively passing effluent from the secondary effluent launder 35 tothe bed of the trickling filter or biologic treating means. From the sump or receiving section 12, of the lter casing 1|, effluent from the filter bed is passed along the pipe or section conduit 80 from which it is conveyed by pump 8| into the pipe section 82 and valve-controlled branches 83 and 84 selectively and respectively into the feed pipe 6 and thusly into the feed-receiving and distributing means 24 for the primary compartment and into the liquid-distributing means 3| of the secondary compartment. The pipe section, 83, pump 8|, pipe section 82 and the valve-controlled pipe Section 83 constitute means for selectively passing and delivering filter effluent into the feed-receiving and distributing means for the primary compartment. Likewise, the pipe section 80, the pump 8|, the pipe section 82 and the valve-controlled section 84 constitute means for selectively passing and delivering filter effluent into the liquid-receiving and distributing means for the secondary compartment.

From thatwhich has preceded, it will be manifest that partially treated supernatant liquid from the primary collecting launder and claried supernatant liquid from the secondary effluent launder is caused to mingle and be passed in selected quantities to the bed of the biologic treating means and that the biologicallytreated effluent from this bed can be selectively passed some to the rear end of the primary compartment and some into the rear ond section of the secondary compartment and that the liquid in each compartment is held in condition favorable to the sedimentation of settleable solids therein.

It will also be noted that if and when desired a sufficiently large quantity of liquidV can. be passed as from the collecting launder 30, or from the collecting launder 3|! and the efiluent launder 35, whereby a relatively large quantitycan be delivered into the secondary distributing means 3|, to wit. in quantity greater than the amount passing into the effluent launder 35 whereby there System of Figures 4 and 5 In this system the biologic treating means is in the form of a trickling lter having a bed of will be a resulting back flow of liquid from the secondary compartment to the primary compartment, all of this taking place even though there is a release from the effluent launder of a quantity of liquid corresponding to the quantity of liquid supplied for treatment.

The valve-controlled pipe line 13,` thepipe sections 11 and 18p, the liquid-distributing head 19, the filter sump 12, the conduit 80, the pump 8|, the pipe section 82, and the valve-controlled pipe section 84 may be viewed as collectively consti-- tuting means embodying a pump for passing at will any desired quantity of liquid from the '-pridiscrete material 18 withina containing structure 1| having a collecting section 12 for receiving filter effluent trickling thereinto. This tricklling filter is at elevation substantially higher than that of the general level of the liquid within the tank. The elevation of the trickling filter is sufficiently high whereby" the filter bed effluent can flow by gravity from the receiving and collecting section 12 through a valve-controlled pipe 90 into the launder 32 of the liquid-receiving and distributing means 3| for the secondary compartment. This elevated position of the trickling filtertherefore necessitates the employment of means essentially comprising a pump for passing any liquid from, the multi-compartment tank upwardly to and upon the trickling filter bed.

According to the arrangement of this system supernatant liquid from the primary compartment is received in the primary collecting launder 30 and is passed from this launder through pipe or conduit sections 9| and 92 into a basin or well 93. supernatant liquid from the secondary compartment overflows into the effluent launder 35 and a quantity of the overflowed liquid passes from the tank through the outflow pipe 31. The quantity of liquid thus released from the system through the outflow pipe` 31 corresponds to the quantity of incoming feedy that is supplied to the tank by the influent pipe 6 and the feeddistributing means 24. A quantity of the overowed liquid received in the effluent launder 35 is passed by the pipe or conduit sections S4 and 32 into the well 93. In this connection it will be noted that the well receives a quantity of partially treated supernatant liquid of the primary compartment that is passed thereto from the collecting launder 3|! and a quantity of the relatively clarified supernatant liquid of the secondary compartment that overflows into the effluent launder 35 and of which some is passed to this well. The liquids received in this well are either commingled therein or effectively mixed before deliveryl to andfdistribution over the bed of the trickling lter'fa-nd for this reason the basin 93 is sometimes referred to herein as a cornrningling well. The liquid is continuously passed from this `well 93 by a conveying and distributing means comprising pipe or conduit section 95, pump 96, pipe or conduit section 91, and a rotary distributor head B8 by which the thus pumped liquid is relatively uniformly distributed over the top lof the tricklingvrlter bed, or as otherwise expressed.

upon the top of the bed o f discrete material of mary collecting launder 30 into the secondary liquid-distributing means 3| wherebyl Control condition of back-flow from'the secondary compartment through the passageway fil-'into the` primary compartment can be attained. Th`s back-flow tends to discourage and in fact can be relied upon t0 prevent the passage of liquid ma-` terial from the primary compartment into the secondary compartment, a thingwhichwould ordinarily take place if such excess quantity of the biologic treating means.

The tank of this system and the mode of operation of the parts associated therewith will be manifest from that which has preceded. It will be pointed out, however, lthat according to a preferred mode of operation there is a passing of liquid into the commingling well in quantities sumcientpfor a. passing of the commingled liquid to the trickling filter bed and for a like passingl of the trickling lter bed effluent into the liquid feed and distributing means 3| for the secondliquid received in the secondary compartment.

over that released from the secondary compartment were not deliberately planned and attained.

ary compartment 23 in quantities greater than thatof the supernatant liquid passing from said secondary compartment into the effluent launder 35 with the result that there is a certain quantity of back-flow liquid continuously passing from the secondary compartment 23 through the passage area 2| into the primary compartment 22. This back-flow of liquid functions in cooperation with the sediment-transferring mechanism 40 to facilitate the transfer of sedmented material from the secondary compartment towards the primary compartment. The back-flow also resists or avoids any tendency for a counter or forward passage of sedimented material from the primary compartment 22 into the secondary compartment 23.

System of Figures 6 and 7 isms von the, material constituting the bed. In

otheriwords, the biologic .treatingmeans of this l system comprehends that which may be viewed as a primary trickling filter and as Aa secondary filter. 'The primary tricking filter is'y shown con- :nected pnnclpa'ny'm assoclatlon Wlth' the pri' I25` ling lter throgh the medium of the pipe or conduit section |22, the pump |23, the pipe orconmary compartment ofthe tank whereby there is f a., repetitive cycling of the liquid undergoing treatment in the primaryfcompartment and in the primary sfllter. The secondary trickling filter j 'bed is connected in-.association with the second-- ary compartment in a manner whereby the liquid of the secondary compartment is cyclically treated bygrepetitiveipasfsage as between itiand the' As to the secondary section of this system it includes the secondary trickling filter |20 and the secondary compartment of the tank. This trickling filter has the bed of discrete material 10 5 the casing 1| and filter effluent is passed from the collecting section 12 thereof by the pipe or conduit section l2 into the secondary liquid-receiving and distributingnmeans 3|, more particularly into the liquid-receiving launder 32 thereof.

supernatant liquid from the secondary compartment 23 overflows the edge 36 into the efflu- .ent launder 35 from which a quantity thereof is released through the outfiow pipe 31 and passes from the system or `treating unit, While a quanl5 tity thereof is passed through a valve-controlled pipe I |2 and the pipe section |04 into the commingling well |05 previously referred to. The liquid within the commingling well, namely, some of the liquid which is passed thereto from the effluent side of the primary biologic treating means and some of the liquid received thereinto from the effluent launder 35 is passed as commingled liquid from the well |05 and is distributingly delivered to the top of the secondary trickduit section |24 and the rotary distributing head 98 by which it is distributed in a relatively uniform manner'over and upon the top of the sec- 3'0 ondary trickling filter bed.

From that which has preceded it will be manifestv how the kdifferent portions of the systems `can be brought into operative arrangement, but

,I here again attention is called to the fact that g h l v some'of the effluent of the primary -trickling filter g'ggi,ets)eofao-lgr Passed into a' recefing We OI'Pasn that re' `ried-out in the system one can effect a transfer "caves soms Ofrth supernatant hqmdffmmfthe `fof"aquantity of liquid into and'from the liquidsecondarxompafltmnt Wherebyhtweur furtg." 'receiving and distributing means 3| for the sectios as af somgnghg Wen reelvmg glfuafngy' 40 ondary compartment 23 that isgreater than that 0f quld rom epmnary Sec lon of f'heys m" "ofthe liquid which outflows from said compart- I and a quantity of liquid imm scndaiY--sec Y 'ment pastthe overflowweir or edge 36 into the g secondary effluent launder '35 -whereby there is In @he arrangement shown by .thsse figures the ...realized a continual back-flow of liquid from the triclcling filter beds are at elevation substantiallyy 415 Secondary compari-,ment 23 into the primary highs, than-th-at of the normal Surface level Of." l compartment 22. This back-flow or passage of a the. hmm? wlthm tfheftank ',herebxler emuent substantial quantityfofr liquid from a secondary Can-graV-tate and be slectlvely dlstvnbted for or subsequent treating compartmenty of a claripassage black intocertaln COIDaltmnts of the fying tank into a primary or preceding comparttank'or into a rsceimg We 01. basin disposed'n 50 -.ment of s uch'tank and in the same direction as ever, that"an"intercon`nection is p'rovidedwhe'reby tion of the system.

associated relationship to the tank and ;from,

which itis pumped. E i nl.

As to the primary sectionlfnf the system.; this embodies a-prirnary trickling filter: yH30 that' includes a bed ofV discrete materiali'l, and a casing structure 1I- therefor 'having a filter effluent collecting section 1,2 from which the filter efiluent flows by gravity through a pipe or conduit section |0| and a valve-controlled branch |02 toand into tha-t in which `sediment is passed from the secondary or subsequent compartment into the primary.- compartment or preceding compartment of such tank is believed to be new in apparatus or units of this general class and is indicative of a -feature of construction which`can vbe advantageously employedin multi-compartment tanks or clarifying units which may have embodiments of. constructions quite different in appearance the feed pipe or Conduitthence into the primary and arrangement from that shownin the hori- Vdownwardly therefrom through the pipe or con duit section |06 into a well |01 provided for receiving partially treated liquid from the primary compartment. The partially treated liquid is passed from this well I 0? to and distributingly delivered upon the bed 'l0 of the primary trickling filter through the medium of pipe or conduit section |08, the pump |09, pipe or conduit section IIO and the rotary distributor head 98.

zontal tank arrangement described herein.

What is claimed is: 1 `1. Apparatus for the continuous treatment of polluted liquids comprising a sedimentation y tank; partial partitioning means dividing the tank into hydraulically communicating primary and secondary clarifying compartments; means for removing sediment from said compartments; means for feeding polluted liquid to be received by the primary compartment, means for releasing clarified purified effluent from the secondary compartment at a rate corresponding to the rate of feed to the primary compartment, aerobic biologic means for treating impure liquid for de- 76 creasing the biologic oxygen demand of the thus treated liquid, means for transferring a quantity of clarified impure supernatant liquid from the primary compartment to said aerobic means,

means for delivering a quantity of liquid discharged from said aerobic means to the secondary compartment, and pump means for passing liquid intransit from the primary compartment through the aerobic means to the secondary compartment at a rate greater than that at which claried purified liquid is released from the secondary compartment sufficient so that contaminating migration is minimized of impure liquid from the primary compartment past the partition into the treated liquid in the Vsecondary compartment.

2. Apparatus according to claim l with the addition of means for recycling liquid between the secondary compartment and the aerobic means.

3. Apparatus according to claim 1 wherein said sediment removing means comprise means for impelling sedimented material settling from the liquid of the secondary compartment into the lower portion of the primary compartment tobe there joined with sediment settling from the liquid of the primary compartment, and means for removing such joined sediment from the primary compartment.

4. Apparatus for the clarification of' polluted liquids comprising a rectangular tank having a bottom and walls adapted to hold a body of liquid being treated, a partition having a lower edge portion vertically spaced from the bottom of the tank and dividing the tank transversely and functionally into primary and secondary clarifying. compartments but leaving hydraulic communication between them, a sediment sump associated with the primary compartment, means for impelling sediment from both said compartments that collects on the tank bottom whereby sediment from the secondary compartment is passed to the primary compartment and sediment from the primary compartment is passed to the sump, feed-receiving and distributing means for the primary compartment, liquid-receiving and distributing means for the secondary uid to the liquid-receiving and distributing means of the secondary compartment, and means for passing to discard effluent from the effluent launder of the secondary compartment.

5. Apparatus according to claim 4 in which there is means for passing some of the Withdrawn further treated liquid to the feed-receiving and distributing means for the primary compartment, and in which there is means for controlling the amount of effluent passing from the efliuent launder of the secondary compartment. to proportion it relative to the further treated liquid fed to and distributed within saidsecondary compartment whereby there is maintained a hydraulic imbalance that effects a liquid ow from the secondary compartment to the primary compartment.

6. Apparatus for the purification of polluted liquids comprising a tank having a bottom and walls adapted to hold a body of liquid being treated, a partition dividing the tank func- A tionally into primary and secondary clarifying compartments, means providing a submerged flow passage area extending between a lower portion of the secondary clarifying compartment and the primary compartment whereby said compartments are in constant hydraulic communication, means for feeding each compartment separately, means for supplying liquid to be treated whereby it is ultimately delivered into the primary clarifying compartment through the feeding means therefor, a separate launder for receiving clarified effluent from each compartment, a sediment sump for and directly` below only liquid within the primary compartment, means for passing sedimented material from said sump, a primary biologic trickling filter bed, means for passing effluent from the primary compartment to the bed and/for returning filterbed discharge as augmented feed to that compartment, a secondary biologic trickling filter bed, means for passing a quantity of effluent from the secondary compartment to the secondary filter-bed and for returning lter-beddisch'arge to that compartment, means for passing a quantity of effluent from the secondary compartment to discard, and combined means for impelling sediment from both the secondary and primary compartments to said sump while avoidingv sliding passage of sediment from the primary to the secondary compartment.

7. In operative combination a liquid-holding tank of the class described having a bottom, a marginal wall rising therefrom, lpartitioning means functionally dividing\the liquid-holding region of the tank into primary and secondary compartments in constant hydraulic communication through the passage area hereafter referred to, and means providing passage area leading from the lower portion of the secondary compartment toward the primary compartment; feed-receiving and distributing means for said primary compartment; supernatant liquid-collecting means disposed at the upper portion of said primary compartment; liquid-distributing means for said secondary compartment; efiiuent collecting means receiving supernatant liquid of said secondary compartment and having an overflow level disposed at elevation sufficiently high for determining the normal surface level of the liquid within the tank; means for lmpelling sedi- 'mary compartment; means for passing sedimented material from the primary compartment; means comprising a pump for passing liquid from said supernatant liquid-collecting means of the primary compartment to said secondary liquid-distributing means in v quantity greater than that of the quantity of liquid overflowing into said secondary effluent collecting means for thereby realizing a certain back-flow of liquid from the secondary compartment through said passage area. into said primary compartment.

8. A unit as defined in and by claim 7, in which there is included as part of the means that includessaid pumpv a branch for passing a quantity of the thereby pumped liquid to the primary feed-receiving and distributing means.

9. A liquid-holding settling tank having a parv tial partition dividing the tank into functionally separate primary and secondary compartments that are in constant hydraulic communication through a passagearea left because of the partition being only a partial one, liquid distributing means for and corresponding to each compartment, means by which initially supplied incoming liquid is passed to the liquid-distributing means for the primary compartment, supernatant collecting means at the upper portion of and serving only the primary compartment, supernantant collecting means at the upper portion of and serving only the secondary compartment, means leading from the collecting means of the secondary compartment for releasing from the tank as clarified supernatant liquid a quantity of liquid corresponding to the quantity of initially supplied incoming liquid that is passed to the liquid-distributing means of the primary compartment, common sludge removal means for said compartments, and-mechanical means for establishing and maintaining a positively irnpelled flow of liquid from the collecting means for the primary compartment into the liquiddistributing means of the secondary compartment suicient in quantity to establish back-flow from the secondary compartment through said passage area and `into the primary compartment,

10. A liquid-treating tank for gravity separation of settleable solids from liquids, partitioning means therein providing only a partial partition by which the interior liquid-holding portion oi.' the tank is divided into a feed-receiving primary compartment and a subsequent secondary compartment, which compartments are in constant hydraulic communication through passage area below a lower edge portion oi the partitioning means that is spaced from an underlying bottom portion of the tank, liquid feed means and liquid withdrawal means for each compartment, means for withdrawing liquid from the initial feed-receiving compartment and for delivering the thus withdrawn liquid into the secondary compartment for continuously maintaining. a back flow of liquid from the secondary compartment through said passage area into the feedreceiving primary compartment, a sump in the bottom of the tank and having extent under the liquid undergoing sedimentation in the primary compartment, means for impelling sedimented material from diverse portions and the lower sections of the primary and secondary compartments towards and into said sump, andmeans for passing sedimented material from within said sump to a region outside of the tank,

ANTHONY `J. FISCHER. WILLIAM C. WEBER. 

